Why "learn the empty palace" before storing anything in it?

So the route is automatic — you can mentally walk all the loci in order (and backwards) with zero hesitation before you add cargo.

If you're still unsure which locus comes after the sofa while also trying to recall what you put there, both fail. So first: walk the empty journey a few times until the sequence of places is effortless — forwards and, ideally, backwards. Only then start placing images. A rehearsed empty palace is a reusable, reliable container; a shaky one leaks.